CVE-2024-35814: swiotlb: Fix double-allocation of slots due to broken alignment handling

Vulnerability summary

CVE-2024-35814 is a high (CVSS 8.8) Double Free vulnerability in linux. EPSS estimates a 0.24% chance of exploitation in the next 30 days, higher than 14.6% of scored vulnerabilities.

Timeline

1. 17-05-2024
   PublishedVulnerability first disclosed.
2. 05-08-2026
   Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: swiotlb: Fix double-allocation of slots due to broken alignment handling Commit bbb73a103fbb ("swiotlb: fix a braino in the alignment check fix"), which was a fix for commit 0eee5ae10256 ("swiotlb: fix slot alignment checks"), causes a functional regression with vsock in a virtual machine using bouncing via a restricted DMA SWIOTLB pool. When virtio allocates the virtqueues for the vsock device using dma_alloc_coherent(), the SWIOTLB search can return page-unaligned allocations if 'area->index' was left unaligned by a previous allocation from the buffer: # Final address in brackets is the SWIOTLB address returned to the caller | virtio-pci 0000:00:07.0: orig_addr 0x0 alloc_size 0x2000, iotlb_align_mask 0x800 stride 0x2: got slot 1645-1649/7168 (0x98326800) | virtio-pci 0000:00:07.0: orig_addr 0x0 alloc_size 0x2000, iotlb_align_mask 0x800 stride 0x2: got slot 1649-1653/7168 (0x98328800) | virtio-pci 0000:00:07.0: orig_addr 0x0 alloc_size 0x2000, iotlb_align_mask 0x800 stride 0x2: got slot 1653-1657/7168 (0x9832a800) This ends badly (typically buffer corruption and/or a hang) because swiotlb_alloc() is expecting a page-aligned allocation and so blindly returns a pointer to the 'struct page' corresponding to the allocation, therefore double-allocating the first half (2KiB slot) of the 4KiB page. Fix the problem by treating the allocation alignment separately to any additional alignment requirements from the device, using the maximum of the two as the stride to search the buffer slots and taking care to ensure a minimum of page-alignment for buffers larger than a page. This also resolves swiotlb allocation failures occuring due to the inclusion of ~PAGE_MASK in 'iotlb_align_mask' for large allocations and resulting in alignment requirements exceeding swiotlb_max_mapping_size().

• CWE-415Double FreeThe product calls free() twice on the same memory address.
• CWE-119Improper Restriction of Operations within the Bounds of a Memory BufferThe product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary.
• CWE-1055Multiple Inheritance from Concrete ClassesThe product contains a class with inheritance from more than one concrete class.